Compressed Air Generator Unit for a Vehicle and Method for the Control Thereof

ABSTRACT

A compressed air generator system for a vehicle includes at least one drive motor having a compressed air generator for generating compressed air, an electrical motor coupled to the compressed air generator for driving the compressed air generator; a controllable coupling for coupling the compressed air generator to the at least one drive motor, a control device for controlling the compressed air generator unit, and a synchronization device for synchronizing a compressed air generator rotational speed of the compressed air generator and an output rotational speed of the at least one drive motor. The controllable coupling is switchable with a synchronized compressed air generator rotational speed and output rotational speed. A corresponding method controls the compressed air generator system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International Application No. PCT/EP2008/007206, filed Sep. 4, 2008, which claims priority under 35 U.S.C. §119 from German Patent Application No. DE 10 2007 042 319.7, filed Sep. 6, 2007, the entire disclosures of which are herein expressly incorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a compressed-air generating system of a vehicle, and to a method for controlling such a system.

Compressed-air generating systems of this kind currently employ compressors and/or compressed-air generators for generating compressed air, for example for a service brake in a vehicle such as a commercial vehicle, which are driven exclusively directly by the drive motor of such a vehicle. In commercial vehicles, the drive motor is in most cases an internal combustion engine in the form of a diesel engine. For the purpose of saving energy, solutions with a mechanical disconnection clutch which is arranged between the drive and the compressed-air generator are known to the applicant.

In the case of vehicles which are equipped with a hybrid drive, it is necessary for the supply of compressed air to be ensured even when the drive motor is switched off. Electrically driven compressed-air generators are used in this case. The drive is in the form of an electric motor which is equivalent to a disengaged clutch in the switched-off state, with no power being lost in this state. However, during normal operation, an electric motor of this type has a considerable disadvantage since the conversion of mechanical energy into electrical energy and vice versa causes energy loss.

The object of the present invention is therefore to provide a compressed-air generating system which eliminates or reduces the above-mentioned disadvantages and exhibits minimal energy consumption in an electrically driven compressed-air generator.

The object is achieved by a compressed-air generating system and method of controlling same, having at least one drive motor. A compressed-air generator is provided for generating compressed air. An electric motor, which is coupled to the compressed-air generator, drives the compressed-air generator. A controllable clutch couples the compressed-air generator to the at least one drive motor. A control device controls the compressed-air generating system, and a synchronizing device synchronizes a rotation speed of the compressed-air generator and an output rotation speed of the at least one drive motor. The controllable clutch is shiftable when the compressed-air generator rotation speed and the output rotation speed are synchronized.

According to the invention, it is possible to also drive a compressed-air generator, which is driven by an electric motor, by a drive motor of the vehicle via a disconnection clutch or controllable clutch. The clutch is engaged only when the compressed-air generator is accelerated by the electric motor to an output rotation speed of the drive motor of the vehicle or has been synchronized with the output rotation speed.

This therefore has the advantageous effect that the energy consumption for generating compressed air in a compressed-air generator with an electric drive is reduced, since the electric motor is switched to an idling state as soon as the compressed-air generator is driven by the drive motor, so that no further losses arise.

Synchronization of the rotation speed of the compressed-air generator with the output rotation speed of the drive motor has the effect that no frictional losses occur when the clutch is engaged. As a result, the maintenance intervals for a friction clutch are advantageously extended.

A method according to the invention for controlling a compressed-air generating system of a vehicle with at least one drive motor includes the following method steps:

(V1) driving a compressed-air generator with an electric motor in order to generate compressed air;

(V2) synchronizing a rotation speed of the compressed-air generator with an output rotation speed of the at least one drive motor; and

(V3) shifting a controllable clutch when the rotation speeds are synchronous, in order to couple the compressed-air generator to the drive motor in order to generate compressed air.

Without this synchronization, a friction clutch would have to be designed to be very sturdy since the compressed-air generator exhibits high peak torques. In a preferred embodiment, provision is made for the controllable clutch to be in the form of a positively locking shiftable clutch. This permits an advantageously simple configuration of a shift clutch with high transmission torques. This positively locking shiftable clutch may be, for example, a bolt clutch or a toothed clutch. A particularly robust design is possible particularly when this shift clutch is a dog clutch.

In a further embodiment, the synchronization device is provided with: a first determination device for determining the rotation speed of the compressed-air generator; a second determination device for determining the output rotation speed of the at least one drive motor; a comparison device for comparing the compressed-air generator rotation speed and the output rotation speed; an electric motor control unit for controlling the electric motor; and a shifting unit for shifting the controllable clutch when the compressed-air generator rotation speed and the output rotation speed are synchronized.

Measurement signals and information relating to the rotation speeds of the drive motor and/or of an output of the drive motor, for example on a gear mechanism of a drive train of the vehicle, which are already present in the vehicle can advantageously be used in this case. The electric motor control unit may use, for example, rotation speed signals of the electric motor from its own rotation speed sensors, in order to determine the compressed-air generator rotation speed. Therefore, the shift clutch can be subjected to intelligent control in order to always ensure reliable switching on of the compressed-air generator when compressed-air is required. The control device may also report information which is important for the driver of the vehicle and display such information for him.

In a further embodiment, provision is made for the electric motor control unit to be designed to set the compressed-air generator rotation speed, and to set an idling mode and a generator mode of the electric motor. When the drive motor of the vehicle drives the compressed-air generator when the shift clutch is engaged, the electric motor is switched to an idling state. That is to say it forms only a low rotation resistance in its bearings and co-rotates freely. However, in another embodiment, it is also possible for the electric motor to be switched to a generator state, that is to say the electric motor can serve as an additional power source in this case and, for example, charge the vehicle battery or operate as an emergency power source.

In a further embodiment, the controllable clutch is coupled to an output of a drive train of the vehicle. This may be, for example, on a gear mechanism of the drive train of the vehicle. As a result, it is possible for a drive torque for the compressed-air generator to be produced by the wheels of the vehicle in a manner driven by way of the drive train even when the motor is switched off or at a low drive motor rotation speed when the vehicle is coasting.

In a further embodiment, the synchronizing device is a constituent part of the control device, as a result of which space can be saved. In addition, control elements, for example processors, of the control device can take on the tasks of rotation speed determination, comparison, etc.

In a hybrid drive, only the electric motor can drive the compressed-air generator when the drive motors are switched off, with the controllable clutch being disengaged.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE is a schematic block diagram of an exemplary embodiment of a compressed-air generating system according to the invention.

DETAILED DESCRIPTION OF THE DRAWING

In the single FIGURE, solid lines between functional units represent a transmission of force, for example by torque transmission, and dashed lines represent control connections, for example for control signals and/or measurement signals.

A vehicle, which is only schematically indicated here, has, in this example, a hybrid drive with a first drive motor 2, for example an internal combustion engine in the form of a diesel engine, and a further drive motor 2′ in the form of an electric motor or machine. These drive motors 2, 2′ are coupled to a drive train 13 which includes a gear mechanism 14 and a drive axle 18, in which a differential gear mechanism and two wheels are provided. A motor controller 19 is connected to the drive motors 2, 2′ and to the gear mechanism 14.

In this example, the gear mechanism 14 is equipped with an output 15 for coupling to a compressed-air generating system 20 via a clutch drive KA, for example a shaft.

The compressed-air generating system 20 has a compressed-air generator 1 or compressor, which is coupled to an electric motor 3 and to a controllable clutch 4, and a control device 5 for controlling the compressed-air generating system 20. The compressed-air generator 1 draws in intake air AL during operation, compresses this intake air and conveys it as compressed air DL to a compressed-air reservoir 7, from which the compressed air DL is taken as required, for example for a brake system of a commercial vehicle.

The control device 5 has a synchronizing device 6 with a first determination device 8 for a compressed-air generator rotation speed d1, a second determination device 9 for an output rotation speed d2 of the drive motor 2, 2′ (in this case the output 15), a comparison device 10, an electric motor control unit 11 and a shifting unit 12.

The control device 5 is also coupled with pressure sensors 16 for detecting a pressure of the intake air AL at the compressed-air generator 1 and a pressure of the compressed air DL (either at the compressed-air generator 1 or at the compressed-air reservoir 7). Rotation speed sensors 17 on a coupling shaft between the electric motor 3 and the compressed-air generator 1 and on a coupling shaft between the compressed-air generator 1 and the controllable clutch 4 are likewise coupled to the control device 5 and transmit measurement signals of the associated rotation speeds. The electric motor 3 can be equipped with an integrated rotation speed sensor, (indicated by a branched control path). The control unit 5 is also coupled to the controllable clutch 4 and to the motor controller 19.

The functioning of the individual functional units of the compressed-air generating system 20 is described below. One of the drive motors 2, 2′ is in operation. The controllable clutch 4 is initially disengaged. When compressed air is required in the compressed-air reservoir 7, the first determination device 8 determines the output rotation speed d2 of the drive motor 2, 2′ via the connection to the motor controller 19. The second determination device 9 determines the rotation speed d1 of the compressed-air generator 1. The comparison device 10 compares the rotation speeds d1 and d2. When there is a difference, the comparison device generates a signal for the electric motor control unit 11 which drives the electric motor 1 and sets it to a rotation speed d1 corresponding to the output rotation speed d2, that is to say it is synchronized with this. The shifting unit 12 then connects the controllable clutch 4, that is to say the controllable clutch is engaged and couples the drive motor 2, 2′ to the compressed-air generator 1 via the output 15 and the gear mechanism 14. The drive motor 2, 2′ now drives the compressed-air generator 1 and the electric motor 3 is switched to an idling state by the electric motor control unit 11.

If the drive motor 2, 2′ is not in operation and pressure is required, only the electric motor 3 is switched on and drives the compressed-air generator 1.

Synchronization of the rotation speeds d1 and d2 makes it possible for the controllable clutch 4 to be designed with a robust configuration as a shiftable positively locking clutch. This may be, for example, a dog clutch, a toothed clutch or a bolt clutch with an electric drive.

It is therefore also possible to use a friction clutch or a combination including a dog clutch and a friction clutch, for example as a kind of synchronizer ring.

The control device 5 can also have a signalling device which, for example, provides information for the driver. This may be, for example, a fault message, maintenance message, etc.

Table of Reference Numerals 1 Compressed-air generator 2, 2′ Drive motor 3 Electric motor 4 Clutch 5 Control device 6 Synchronizing device 7 Compressed-air reservoir 8 First determination device 9 Second determination device 10 Comparison device 11 Electric motor control unit 12 Shifting unit 13 Drive train 14 Gear mechanism 15 Output 16 Pressure sensor 17 Rotation speed sensor 18 Drive axle 19 Motor controller 20 Compressed-air generating system AL Intake air DL Compressed air d1 Compressed-air generator rotation speed d2 Output rotation speed KA Clutch drive

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 

1. A compressed-air generating system of a commercial vehicle with at least one drive motor, the system comprising: a compressed-air generator for generating compressed air; an electric motor operatively coupled to the compressed-air generator for driving the compressed-air generator; a controllable clutch operatively configured to couple the compressed-air generator to said at least one drive motor; a control device operatively configured to control the compressed-air generating system; a synchronizing device operatively configured to synchronize a rotation speed of the compressed-air generator and an output rotation speed of said at least one drive motor; and wherein the control device controls said controllable clutch to be shiftable when the compressed-air generator rotation speed and the output rotation speed of said at least one drive motor are synchronized by the synchronization device.
 2. The compressed-air generating system according to claim 1, wherein the synchronizing device comprises: a first determination device for determining said rotation speed of the compressed-air generator; a second determination device for determining said output rotation speed of said at least one drive motor; a comparator for comparing the compressed-air generator rotation speed and the output rotation speed; a control unit for the electric motor, the control unit being configured to control the electric motor; and a shifting unit operatively configured for shifting the controllable clutch when the compressed-air generator rotation speed and the output rotation speed are synchronized.
 3. The compressed-air generating system according to claim 1, wherein the electric motor control unit is operable to set a rotation speed of the compressed-air generator and to set idling and generator modes of the electric motor.
 4. The compressed-air generating system according to claim 1, wherein the controllable clutch is a positively locking, shiftable clutch.
 5. The compressed-air generating system according to claim 4, wherein the controllable clutch is a dog clutch.
 6. The compressed-air generating system according to claim 1, wherein the controllable clutch is coupled to an output of a drive train of the commercial vehicle.
 7. The compressed-air generating system according to claim 1, wherein the synchronizing device is incorporated into the control device.
 8. A method for controlling a compressed-air generating system of a vehicle with at least one drive motor, the method comprising the acts of: driving a compressed-air generator with an electric motor in order to generate compressed air; synchronizing a rotation speed of the compressed-air generator with an output rotation speed of the at least one drive motor; and shifting a controllable clutch when the rotation speeds are synchronous, in order to couple the compressed-air generator to the at least one drive motor in order to generate the compressed air.
 9. The method according to claim 8, wherein the act of synchronizing comprises the acts of: determining a rotation speed of the compressed-air generator; determining an output rotation speed of the at least one drive motor; comparing the determined rotation speeds and generating a control signal for an electric motor control unit; and actuating an electric motor by the electric motor control unit based on the control signal relating to the output rotation speed of the drive motor for synchronizing the compressed-air generator rotation speed with the output rotation speed.
 10. The method according to claim 8, wherein the act of shifting comprises the acts of: engaging the controllable clutch via a shifting unit; and controlling the electric motor in an idling state by way of the electric motor control unit.
 11. The method according to claim 9, wherein the act of shifting comprises the acts of: engaging the controllable clutch via a shifting unit; and controlling the electric motor in an idling state by way of the electric motor control unit.
 12. The method according to claim 8, wherein the act of shifting comprises the acts of: engaging the controllable clutch via a shifting unit; and controlling the electric motor in a generator state by the electric motor control unit in order to generate electrical energy.
 13. The method according to claim 9, wherein the act of shifting comprises the acts of: engaging the controllable clutch via a shifting unit; and controlling the electric motor in a generator state by the electric motor control unit in order to generate electrical energy. 